Abstract

Xanthine oxidase enzymes are known to catalyze oxidative hydroxylation reactions in variety of biochemical reactions including hydroxylation of various purines and aldehydes. This work is focused on predicting the transition state structure and probing the reaction mechanism of formate oxidation by using xanthine oxidase. The events at the transition state and mechanistic route were probed using DFT method with b3lyp level of theory. LANL2DZ and 6-31G (d', p’) basis sets were used for molybdenum and none metal atoms respectively. In order to understand the events taking place in the reaction path several parameters such as, energy, charge and bond distance were computed. The transition state of none protonated, single protonated and double protonated formate bound to the active site, respectively, were confirmed at -523.1 S-1, -391.2 S-1 and -734.17 S-1 by the one imaginary frequency. High activation barriers are obtained for transformation of substrate bound to the transition state for none protonated substrate bound to the active site due to the absence of factors that stabilize the accumulation of charge on substrate at the transition state. Oxidation of formate with single protonation was shown to be the most favorable path compared to none protonated and double protonated formate bound to the active site of enzyme. The oxidation of single protonated formate was shown to favor step wise mechanism than concerted mechanism. The study of formate oxidation has mechanistic significance.